The present invention relates generally to implantable medical devices for providing stimulating pulses to selected body tissue, and more particularly, to the lead assemblies connecting such devices with the tissue to be stimulated.
Although it will become evident to those skilled in the art that the present invention is applicable to a variety of implantable medical devices utilizing pulse generators to stimulate selected body tissue, the invention and its background will be described principally in the context of a specific example of such devices, namely, cardiac pacemakers for providing precisely controlled stimulation pulses to the heart. However, the appended claims are not intended to be limited to any specific example or embodiment described herein.
Pacemaker leads form the electrical connection between the cardiac pacemaker pulse generator and the heart tissue which is to be stimulated. As is well known, the leads connecting such pacemakers with the heart may be used for pacing, or for sensing electrical signals produced by the heart, or for both pacing and sensing in which case a single lead serves as a bidirectional pulse transmission link between the pacemaker and the heart. An endocardial type lead, that is, a lead which is inserted into a vein and guided therethrough into a cavity of the heart, includes at its distal end an electrode designed to contact the endocardium, the tissue lining the inside of the heart. The lead further includes a proximal end having a connector pin adapted to be received by a mating socket in the pacemaker. A flexible, coiled conductor surrounded by an insulating tube or sheath typically couples the connector pin at the proximal end and the electrode at the distal end.
With the onset of multi chamber pacing for Congestive Heart Failure (CHF), there has been much discussion and debate in the medical community as to what is the most desirable lead possible for left ventricular (LV) stimulation. The overwhelming opinion of physicians seems to be that the xe2x80x9cbestxe2x80x9d LV lead is the one that is easiest to place and involves the fewest procedures and parts. As a result of recent advancements in techniques and instrumentation, many physicians have become convinced that a lead that is placed with a guidewire, instead of a stylet, is superior.
Investigations have been performed on an LV lead that can be placed using a stylet and such designs have been optimized. In an effort to address the needs of the market as related above, a through hole was drilled in the tip of this stylet driven LV lead and converted into a lead intended to be placed over a guidewire. Unfortunately, it was determined that this over-the-wire (OTW) LV lead was no longer optimum for LV placement. Problems were encountered which included jamming of the guidewire in the coil when trying to advance the lead over the guidewire or when trying to advance the guidewire through the lead. These problems were amplified when the lead was advanced through the tortuous turns of the veins of the left heart. This jamming was due in part to offsetting of the coils (causing an uneven inner diameter), coil compression, and coil elongation. As a result slidability and trackability of the lead were severely sacrificed.
To solve this jamming problem, initially, changes to the coil configuration were considered such as using a larger wire diameter, increasing the inner diameter of the coil, and decreasing the number of filars (individual wires) of the coil. Although some of these configurations were improvements over the original design, the improved results were actually very modest.
It was in light of the foregoing that the present invention was conceived and is now hereby reduced to practice.
The present invention concerns an implantable lead for electrical stimulation of the body. The implantable lead of the invention includes an elongated multi-lumen tube with a distal tip electrode having a longitudinally extending central bore. A cable conductor is received in one lumen of the multi-lumen tube for electrical connection to the distal tip electrode and an elongated polymeric tubular liner having a coefficient of friction when measured on steel in the range of 0.01 to 0.1 is received in another lumen of the multi-lumen tube generally aligned with the bore of the distal tip electrode for freely receiving a guidewire through the tubular liner and through the bore of the distal tip electrode. An electrically conductive proximal pin is attached to the multi-lumen tube distant from the distal tip electrode and, in one embodiment, the cable conductor and the proximal end of the polymeric tubular liner are attached to the proximal pin. Initially, the guidewire is implanted into the body along a desired trajectory. With the polymeric tubular liner inserted, first the distal tip electrode, then the remainder of the multi-lumen tube, are slid onto the guidewire such that the guidewire slidably advances within the polymeric tubular liner. Thereupon, the multi-lumen tube is advanced along the guidewire until a desired site is achieved and the guidewire is removed from the body and the multi-lumen tube. In another embodiment, the distal tip electrode has no central bore but the elongated polymeric tubular liner is axially aligned with the distal tip electrode for freely receiving a stylet and is attached with the distal tip electrode.
Due to the limited success achieved when changing the coil configuration and insulation as mentioned above, the present invention resulted from the investigation of an entirely new lead configuration. Instead of using a coil as a liner for guidewire passage, it was decided to investigate use of a liner composed of a suitable polymer with a low coefficient of friction such as polytetrafluoroethylene (PTFE), better known, perhaps, under the trademark TEFLON(copyright), or equivalent. PTFE has a very low coefficient of friction, it elongates minimally under an axial load, and in tubular form has a uniform inner and outer diameter. In vitro and in vivo testing of a silicone lead with a PTFE liner has proved to be very successful. The lead does not jam on the guidewire and the lead tracks in a satisfactory manner over the guidewire through the tortuous bends of the veins of the left heart. Both in vitro and in vivo testing of a polyurethane lead with a PTFE liner have proved successful as well.
In one embodiment of a LV OTW lead with a PTFE liner, the PTFE liner is removable. In such an embodiment, the lead is successfully placed over a guidewire. Next the guidewire is removed and, finally, the PTFE liner is removed. This allows for loading of the liner with barium sulfate or bismuth subcarbonate to increase visibility of the lead under x-ray. These compounds are not commonly used in permanently implanted devices.
In another embodiment, the PTFE liner is placed in the inner diameter of a coil. This prevents the problems that were encountered, as discussed above, with the coil, yet allows for the coil to service the distal tip electrode. Furthermore, the coil increases the visibility of the lead under x-ray. In this embodiment, the PTFE liner may be removed following final placement of the lead.
In another embodiment the lead includes two cable conductors. In this embodiment, one cable conductor services the distal ring electrode (in contrast with a current design which employs tri-lumen tubing receiving two cable conductors) and the other cable conductor services the distal tip electrode. Due to the fact that the cable conductor is not coaxial with the distal tip electrode or the connector pin, a unique electrical connection is required.
Due to the fact that a PTFE liner can be of thinner wall thickness than a coil liner, the overall diameter of a lead embodying the teachings of the present invention can be decreased. This is a desirable feature, especially in the small distal and tributary veins of the left heart. Also, as a result of the smaller diameter, two leads may be placed in the larger veins of the left heart such as the coronary sinus, great cardiac vein, and posterior cardiac vein.
Another embodiment is to use the PTFE liner in a stylet placeable lead. This helps to increase trackability and steerability when placing a left sided lead that is stylet driven for those customers who prefer stylet driven left heart leads. This allows for a decreased overall diameter of right sided leads. With this construction, a smaller introducer can be used to place one lead. The same size introducer used today for placing one lead can thereby be used to place two leads, with the lead being less occlusive to the veins entering the heart.
A primary feature, then, of the present invention is the provision of an improved lead assembly for implantable medical devices providing stimulating pulses to selected body tissue.
Another feature of the present invention is the provision of such a lead assembly with an elongated polymeric liner for insertion of a guidewire for enhanced trackability and steerability of the lead.
Yet another feature of the present invention is the provision of such a lead assembly wherein the polymeric liner has a coefficient of friction in the range of 0.01 to 0.2.
Still another feature of the present invention is the provision of such a lead assembly wherein the polymeric liner is loaded with a radio opaque substance to increase lead visibility under x-ray.
Yet another feature of the present invention is the provision of such a lead assembly with a polymeric liner that can be fully removed after placement of the lead.
Still a further feature of the present invention is the provision of such a lead assembly with a polymeric liner inside the inner diameter of a conductor coil provided for electrically servicing the distal tip electrode.
Yet a further feature of the present invention is the provision of such a lead assembly with a polymeric liner that has a unique electrical connection between a non coaxial cable conductor and the distal tip electrode.
Still another feature of the present invention is the provision of such a lead assembly with a polymeric liner that has a unique electrical connection between a non coaxial cable and the proximal connector pin.
Another feature of the present invention is the provision of such a lead assembly with a polymeric liner that has a reduced diameter for optimum placement in the small distal and tributary veins of the left heart.
A further feature of the present invention is the provision of such a lead assembly with a polymeric liner that has a reduced diameter to allow for placement of more than one lead in the veins of the left heart.
Still another feature of the present invention is the provision of such a lead assembly with a polymeric liner for insertion of a stylet for enhanced trackability and steerability of the lead.
Yet another feature of the present invention is the provision of such a lead assembly with a polymeric liner for insertion of a stylet and placement in the right heart with a decreased overall diameter.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.